The present invention relates to an optical scanner that forms an optical path for an image light emitted from a light source, and to an image forming apparatus according to an electrophotography method such as a printer provided with a photoreceptor that undergoes an exposure to an image light from the optical scanner.
An image forming apparatus performing an image forming process according to the electrophotography method is provided with an optical scanner that causes a photoreceptor to be exposed to an image light. The optical scanner includes a light source, a scan means and an optical element. The light source emits an image light that is modulated by image data. The scan means scans the image light in a predetermined scan plane. The optical elements, which are lense(s) and mirror(s), include an incident optical element that deflects the image light emitted from the light source to lead to the scan means and an outgoing optical element that deflects at a uniform velocity the image light deflected at a constant angular velocity by the scan means to lead to the photoreceptor.
These light source, scan means and optical elements are housed in a casing with a shading property in order to prevent the image light from being affected by external light. In conventional optical scanners as disclosed in Japanese Patent Unexamined Publication No. 2001-183573 bulletin, for example, a casing made of resin molded components or the like, which is a thermoplastic material, has been used due to requirements for weight and cost reductions. The casing is provided with a plurality of support members integrally formed on its inside surface, and the support members support the light source, the scan means and the optical elements. The optical scanner forms, within the casing, an optical path for the image light from the light source by way of the incident optical element(s), the scan means and the outgoing optical element(s), wherefrom the light goes outside the casing.
Meanwhile, in an image forming process according to the electrophotography method, an exposure step, a development step, a transfer step and a fusing step are carried out sequentially in this order. The optical scanner forms an electrostatic latent image on the photoreceptor by subjecting it to an exposure to an image light in the exposure step. The electrostatic latent image is made visible as a toner image in the development step. The toner image is transferred onto paper in the transfer step. After the transfer step, the paper is heated and pressed in the fusing step, and thus the toner image is fixed on the paper.
For this purpose, the image forming apparatus according to the electrophotography method is equipped with a fuser unit that raises a surface temperature of the paper to a value higher than a fusing temperature of the toner. Because of the heat that the fuser unit generates at the time when an image forming process is performed, a temperature inside the image forming apparatus rises.
In addition, the image forming apparatus are provided with motors for supplying rotational motions to photoreceptor drums and conveyance rollers, along with a large number of electrical circuitry components such as driving circuit, control circuit and the like. Due in part to the heat from these motors and also the electrical circuitry components, the temperature inside the image forming apparatus rises.
However, when the temperature inside the image forming apparatus rises due to the heat from the motors, the electrical circuitry components and the fuser unit, deformation of the casing of the optical scanner made of resin, which is a thermoplastic material, occurs, thereby causing a mounting angle of an optical element that is supported through the support member by the inside surface of the casing to change (lean). Leaning of the optical element causes an error in an optical axis of the image light within the casing, and hence causes a deviation in exposure position of the image light on the photoreceptor; and thus image reproducibility deteriorates due to an error of an image position. In an optical scanner used for color image forming comprising a plurality of light emitting devices emitting image lights corresponding to the plurality of respective colors as light sources, errors occur in the exposure positions of the image lights of the respective colors on the photoreceptor due the leaning of the optical elements; and thus image reproducibility deteriorates due to changes in color tones in color images. Notably, leaning of the incident optical element causes a great amount of deviation of the exposure position.
The present invention is directed to providing a optical scanner that is capable of reducing the leaning of the optical elements in the casing, reducing an error in an optical axis of an image light, and thereby preventing the deterioration of image reproducibility, even when a thermal deformation occurred in a casing due to a temperature rise on an image forming process.